The present invention relates to a method of data transmission from a data source to a data sink over a bus system.
A plurality of ready-to-use multimedia bus systems for simultaneous data transmission of multiple audio and video channels are used in accordance with the related art. However, most of these bus systems are not suitable for use in the automotive field because they are too complicated technically and their immunity to vibrations, temperature fluctuations and other external influences is too low. In addition, these systems have modules that are too large for use in the automotive field and therefore they are not used in this field.
According to the related art, the D2B bus system and its successor, the MOST (media oriented systems transport) bus system, are used specifically in the automotive field where components with smaller temporary and fixed memories are used. However, the most important system parameters of the MOST bus are designed for data transmission of audio data.
An object of the present invention is in general to create a means of data transmission of image data from a data source to a data sink over a bus system that can be used in the automotive field, where the additional information required for data transmission over a synchronous bus can easily be integrated into the existing data protocol.
Methods of achieving this object according to the related art are described below.
Data transmission of moving images is also possible by means of an MPEG (motion picture expert groups) compression method.
The fact that the MPEG compression method is subject to loss and thus not suitable for transmission of high quality GUI (graphical user interface) graphics has proven to be a disadvantage of this method. Furthermore, compression in the MPEG compression method is very complicated.
In another method of data transmission of pixel-oriented image data over a MOST bus, another compression method, namely the Lempel-Ziv algorithm, is used. In this method, a data sequence to be compressed is analyzed for repeats of subsequences, with recurring elements being stored in a code table and the subsequences being replaced by an assigned code.
One disadvantage of this known approach is that a table of an unknown size must be created for decompression. Working with large temporary tables is a disadvantage for implementation in embedded systems.
Finally, another method involves compression by means of a run length encoding method, referred to below as the RLE method. If a data stream compressed by an RLE method is transmitted over a bus system, certain additional information must be added to it to allow appropriate processing by a data sink.
The method according to the present invention has the advantage in comparison with the known methods that it provides a simple data protocol for synchronous data buses and a simple and sturdy data transmission of pixel-oriented image data, in particular compressed data with certain additional information over a bus system. An existing data format such as that stored temporarily or permanently within an embedded system is made busable through minor modifications, with the modified data format being compatible with the original data format.
An idea on which the present invention is based is that the method of data transmission over a bus system involves definition of at least one predefined repeat factor in the first data element as a flag for the presence of additional information, where the second data element contains the additional information.
This creates a simple data protocol with which additional information on a compressed data stream is transmitted elegantly over a bus system. In this way, predefined repeat factors are assigned to the specific code to implement the specific protocol. This permits a simple data protocol, e.g., for synchronous bus systems. The additional data volume due to the additional information can thus be reduced.
According to a preferred refinement, the repeat factors are natural numbers in an interval from xe2x80x9c0xe2x80x9d to xe2x80x9c255.xe2x80x9d This is obtained from the 256 different data values in an 8-bit byte.
According to another embodiment, the predefined repeat factor is preferably xe2x80x9c0xe2x80x9d and/or xe2x80x9c1xe2x80x9d as a flag for the presence of additional information. In this modification, coding is preferably performed by the repeat factors which do not have any meaning per se as the identifiers flagging a repeat of a certain data.
According to another preferred refinement, additional repeat factors different from xe2x80x9c0xe2x80x9d and/or xe2x80x9c1xe2x80x9d are used as flags for the presence of additional information which is preferably in the upper range of the above-mentioned interval. Thus, additional repeat factors are available for the case when two repeat factors are not sufficient. Since data usually occurs with smaller repeats, higher repeat factors can be selected in particular.
According to another preferred embodiment, the method of data transmission of compressed data is used, where the data to be transmitted is designed as pixel-oriented image data, for example. Thus, data transmission of compressed image data is guaranteed.
According to another preferred embodiment, the bus system is designed as a synchronous MOST bus system. This bus system is intended for use in the automotive field in particular.
According to another preferred refinement, the additional information represents among other things the beginning or the end of a logical data unit, a neutral data element as a filler, the sender or the recipient of a data unit, additional information about the type of run length encoding used, additional information about error detection or additional information about general bus management. Such additional information must be transmitted over a synchronous bus system together with the compressed data stream so that the data transmitted can be processed accordingly by the data sink.